1. Field of the Invention
The present invention relates to an optical system for a camera; and, more particularly, to an optical system for a camera in which a wide-angle of view can be implemented by using the number of lenses as small as possible and inter-compensation can be achieved with respect to contraction and expansion of plastic lenses caused by external temperature.
2. Description of the Related Art
In recent, a mobile communication means (e.g., mobile communication terminal, PDA, and smart phone) has a tendency toward increase in its use and diversification of services provided through communication technologies. In line with this, the mobile communication means has incorporated additional functions in various types, in addition to basic communication functions. A camera function of the additional functions is most frequently mounted on a mobile communication means.
Such a camera becomes gradually small and thin with the miniaturization of camera-mounted devices. In particular, with the gradually increased use of a front/rear monitoring camera for an automobile or of a CCTV for external monitoring, an optical system of a wide-angle of view has been demanded which has a compact size and provides image information in wide ranges.
An optical system of a wide-angle of view should be used as an optical system for external monitoring or rear monitoring, because such a monitoring optical system should take a picture from the outside in wide ranges. Additionally, an optical system should be designed to be light enough to identify a subject even in a dark environment.
Optimal conditions for design of the light optical system are to use glass lenses with spherical surfaces which have superior optical transmittance and refractive indexes. However, it is difficult to design compact and inexpensive optical system in consideration of cost for manufacturing a monitoring camera.
Therefore, in an optical system mounted on a monitoring camera, plastic lenses advantageous for molding should be used and the number of the lenses should be as small as possible, in order to achieve miniaturization and reduction in its price. However, an optical system designed in the prior art fails to satisfy the optimal conditions, because plastic lenses with lower optical performance are used in the optical system. Moreover, reduction in the number of lenses decreases the degree of freedom in design of optical systems.
Meanwhile, at the time of designing an optical system of a wide-angle of view in the prior art, lenses of eight or more are generally necessary and the entire length of the optical system has no choice but to be elongated. That is, in the prior art, it is difficult to satisfy conditions of miniaturization and competitive cost.